Mechanical seal without elastomers

ABSTRACT

A seal that provides sealing between a rotatable shaft and a housing has a stationary part for connection to the housing and a rotary part for rotation with the shaft. The rotary part includes a sleeve for mounting on the shaft. One end of the sleeve is provided with a non-elastometric sealing arrangement. The sealing arrangement has sealing surfaces for contacting outer circumferential surfaces of the sleeve and the shaft as well as means for effecting sealing engagement between each of said sleeve and said shaft and a respective sealing surface.

RELATED APPLICATIONS

The present application is a 35 U.S.C. §371 national phase applicationof PCT International Application No. PCT/GB02/00949, having aninternational filing date of Mar. 8, 2002, and claiming priority toGreat Britain Patent Application No. 0105715.7, filed Aug. 3, 2001, thedisclosure of which is incorporated herein by reference in theirentireties. The above PCT International Application was published in theEnglish language and has International Publication No. WO 03/014602 A1.

BACKGROUND OF THE INVENTION

This invention relates to mechanical seals and especially cartridgemechanical seals which use compressed packing materials and notelastomers to create secondary sealing points.

A Mechanical seal comprises a “floating” component which is mountedaxially movably around the rotary shaft of, for example, a pump and a“static” component which is axially fixed, typically being secured to ahousing. The floating component has a flat annular end face, i.e. itsseal face, directed towards a complementary seal face of the staticcomponent. The floating component is urged towards the static componentto close the seal faces together to form a sliding face seal, usually bymeans of one or more spring members. In use, one of the floating andstatic components rotates; this component is therefore referred to asthe rotary component. The other of the floating and static componentsdoes not rotate and is referred to as the stationary component.

Those seals whose floating component is rotary are described as rotaryseals. If the floating component is stationary, the seal is referred toas a stationary seal.

If the sliding seal between the Rotary and Stationary components areassembled and pre-set prior to despatch from the Mechanical sealmanufacturing premises, the industry terminology for this is “cartridgeseal”. If the Rotary and Stationary components are despatchedindividually (unassembled) form the Mechanical Seal manufacturingpremises, the industry terminology for this is “component seal”.

Mechanical seals often include elastomeric members to seal static andsemi-dynamic surfaces. In certain seal designs such elastomeric membersmay be replaced with packing materials, which form a compression sealbetween two or more surfaces.

For the clarity of this invention the term elastomer may be thought ofas on o-ring, lip seal, wiper seal or a similar component which has anelastomeric membrane or structure. Likewise, a packing material may bethought of as graphite, PTFE or a material, which may be compressed,often to change its density, to create a seal between two or moresurfaces. Such materials are considered to have no, or very littleelastomeric membrane.

Mechanical seals are used in all types of industries to seal a varietyof different process media and operating conditions.

Such operating conditions range for high temperatures, pressures orparticularly aggressive chemicals. In such cases it is imperative thatthe correct selection of materials, used in the mechanical sealconstruction, is made.

Elastomers are often the weakest link in the mechanical sealconstruction. This is due to the fact that they need to be chemicallycompatible with the sealed media and withstand various operatingconditions. Furthermore, elastomers often degrade when subjected tohigh/low temperatures or pressures. This often limits the mechanicalseal life.

SUMMARY OF THE INVENTION

It is considered to be particularly advantageous to create a mechanicalseal design with no elastomeric sealing members. This removes theweakest link thereby helping to extend seal live.

It is also considered extremely advantageous to create a mechanical sealdesign with no elastomeric sealing members that will physically fitinside a small radial cross sectional space in a cartridge seal format.A prior art single cartridge mechanical seal design, which removes theelastomeric sealing member, is shown in FIG. 1.

The rotary and axially floating seal face (1) is spring biased towards astatic stationary seal face (2). The rotary face (1) is allowed to slideon the static seal face (2). The interface between the rotary seal face(1) and stationary seal face (2) forms sealing area (3). This sealingarea (3) is the primary seal that prevents the process media (4) fromescaping from the process chamber (5).

At the process side of the deal, denoted as inboard, the detachableremovable rotary seal assembly (6) is secured to a sleeve (7) withscrews (8). A compression packing seal (9) is formed between the clampring (10) and rotary seal face drive end (11) using screws (12). Therotary seal assembly (6), screws (8 and 12), packing (9) and clamp ring(10) from the detachable assembly (13). From FIG. 1 this detachableassembly (13) is fitted to the mechanical seal from the left-hand sidedue to the radially outwardly extending portion of sleeve (7) on theoutboard side. The rotary compression packing (9) creates the first ofthree secondary sealing areas.

The second secondary sealing area (14) is formed between stationary sealface (2) and stationary gland (15) using a gland compression packing(16). The gland packing (16) is compressed in place by the spring biasof the rotary seal assembly (6) and by the hydraulic force establishedfrom the process media (4) pressure.

At atmospheric side of the seal, denoted as outboard, the sleeve (7)increases radially to accommodate a sleeve compression packing (17). Thepacking (17) is compressed to the shaft (18) by the clamp ring (19) andscrews (20) to from the third secondary sealing area.

Form FIG. 1 it is evident that when radial screws (8) are secured tosleeve (7), the sleeve (7) will radially deform. This creates assemblydifficulties. The deformation can be limited it the radial cross sectionof the sleeve (7) is increased as shown in FIG. 1.

A large proportion of standard process equipment is designed with eithera 0.3125″ (8 mm), 0.375″ (10 mm) or 0.500″ (12 mm) radial cross sectionbetween the shaft (18) and the process chamber (5), depending on theshaft diameter. Radially increasing the cartridge sleeve (7) as shown inFIG. 1 limits where the design can be physically applied.

The materials used in the design shown in FIG. 1 also suffer fromchemical attack problems since the screws (8) and (12) are sited in theprocess media. This could limit seal life and make the designcommercially impractical as exotic alloy screw materials are notcommonly available.

It is therefore considered that a seal design which removes the screws(8) and (12) out of the process media, removes all elastomeric sealingmembers and is offered to fit inside a radially small cross sectionalinboard opening is deemed considerably advantageous.

BRIEF DESCRIPTION OF THE DRAWINGS

From FIG. 1, the screws (8) and (12) could be eliminated by a leaktight, permanent joint fixing the clamp ring (10) to the sleeve (7) androtary seal face drive end (11). However as the sleeve (7) increasesradially on the outboard side to cater for the shaft packing (17) thiswould mean that the design could not be assembled or disassembled forseal repair. The seal features described above are therefore notpossible to accommodate with the existing prior art technology.

The present invention is described by way of example only with referenceto the accompanying drawings, in which:

FIG. 2. is a longitudinal cross section through a mechanical seal of theinvention.

FIG. 3 corresponds to FIG. 2 and is an enlarged partial longitudinalcross section through a mechanical seal of the invention.

FIG. 4 corresponds to FIG. 3 and is an enlarged partial longitudinalcross section through the outboard side of a mechanical seal of theinvention.

FIG. 5 corresponds to FIG. 3 and is an enlarged partial longitudinalcross section through the inboard side of a mechanical seal of theinvention.

FIG. 6 shows an enlarged partial longitudinal cross section of analternate inboard arrangement of the invention with a non-detachableinboard seal face assembly.

FIG. 7 shows a partial cross section of an alternate arrangement of theinvention with a different outboard seal to shaft sealing arrangementwithout the sleeve supporting member.

FIG. 8 shows a partial cross section of an alternate arrangement of theinvention with an optional inboard sleeve supporting member.

FIG. 9 shows a partial cross section of an alternate arrangement of theinvention with a different outboard seal to shaft sealing arrangement.

FIG. 10 shows a partial cross section of an alternate arrangement of theinvention with a different outboard seal to shaft sealing arrangement.

FIG. 11 shows a partial cross section through a double cartridgemechanical seal of the invention.

FIG. 12 shows a longitudinal cross section through a non-mechanical sealdesign.

FIG. 13 shows a partial cross section of an alternate arrangement of theinvention with a different outboard seal to shaft sealing arrangement.

DETAILED DESCRIPTION OF EMBODIMENTS

From FIG. 2, of the invention the rotary and axially floating seal face(1) is spring biased towards a static stationary seal face (2). Therotary face (1) is allowed to slide an the static seal face (2). Theinterface between the rotary seal face (1) and stationary seal face (2)forms sealing area (3). This sealing area (3) is the primary seal thatprevents the process media (4) from escaping from the process chamber(5).

At the process media (4) side of the seal, denoted as inboard, thedetachable removable rotary seal assembly (6) is secured to a sleeve (7)with screws (12). A compression packing seal (9) is formed between thesleeve (7) and rotary seal face drive end (11) using screws (12). Therotary compression packing (9) creates the first of four secondarysealing areas.

The second secondary sealing area (14) is formed between stationary sealface (2) and stationary gland (15) using a gland compression packing(16). The gland packing (16) is compressed in place by the spring biasof the rotary seal assembly (6) and by the hydraulic force establishedform the process media (4) pressure.

At atmospheric side of the seal, denoted as outboard, the sleeve (7) isterminated adjacent to the drive ring (21). A draw ring (22) locatedradially outwardly of sleeve (7) is axially restrained by a circlip(23). The compression packing (24) is located radially outwardly ofsleeve (7) and is compressed between the draw ring (22), spacer ring(26) and drive ring (21) using screws (25). The separate spacer ring(26) is used to facilitate component manufacture. It is considered selfevident that this could be omitted if the profile of the spacer ring(26) is machined into the drive ring (21) to accommodate the angle onthe packing member (24).

The clamp ring (27) compresses the shaft packing (17) when it is securedto the drive ring (21) using screws (28).

The invention illustrated in FIG. 2 therefore offers a cartridgemechanical seal with no elastomeric members which will fit into smallradial cross sections. This is seen as a major advantage.

From FIG. 3 it should be noted that the drive ring (21) has a radialsupport lip (29) that locates into the recess (30) in sleeve (7). As thepacking (24) is compressed it exerts a radial force on the end of thesleeve (7). The support lip (29) in drive ring (21) supports the end ofthe sleeve (7) helping to prevent sleeve (7) distortion.

The process media (4) is allowed enter the radial gap (31) between thesleeve (7) and shaft (18). The process media (4) is sealed by packingmembers (24 and 17). There are no other un-sealed joints, between therespective outboard parts, where the process media (4) contacts.

FIG. 4 illustrates the drive lug (32) in the drive (21) which locatesinto corresponding slots (33) in sleeve (7). Rotational drive from theshaft (18) is transmitted via the redial screws (34) located in theclamp ring (19) through the screws (28) into the drive ring (21) throughthe drive lugs (32) into the sleeve (7), and then into the rotary sealassembly (6) via the screws (12).

This positive drive mechanism is thought to be particularly advantageousin certain applications. Furthermore, the arrangement of the driveacting in the end of the sleeve (7) ensures that the thin cartridgesleeve (7) is not weakened by the introduction of radial slots away fromthe packing ling area (24).

Referring to FIG. 5, it should be noted that sleeve (7) has an elastomergroove (35) positioned at the inboard side in contact with the processmedia (4). This allows a sacrificial component to be installed intogroove (35), if the application dictates. This helps to eliminate thepossibility of process media (4) contamination in radial gap (31),therefore assisting the removal of the cartridge mechanical seal fromthe shaft (18).

FIG. 5 also illustrates a relief (36) extending radially outwardly inthe bore of the sleeve (7). Said relief is positioned in the vicinity ofthe packing member (9). Any radial sleeve (7) deformation occurred whencompressing packing member (9) using screws (12) is accommodated by therelief (36). This is of particular importance when using packing (9)acting on a thin cross section cartridge sleeve (7).

From FIG. 6 an alternate arrangement of the invention may be viewed. Theinboard screws (12), packing (9) and rotary drive end (11) have beenremoved. FIG. 6 illustrates, by way of example only, the rotary sealface assembly (6), in particular the metal bellows spring member (37)has been permanently fixed to the radially outwardly protruding sectionof the sleeve (7). This design is seen to be particularly advantageouswhen chemical attack is of prime consideration as there are no screws(12) in the process media. Therefore all materials in contact with theprocess media can be selected in one or more exotic alloy ornon-metallic combinations.

A person skilled in the art of mechanical seal design will appreciatethat the invention allows many different inboard seal configurationswhile allowing a mechanical cartridge seal, with no elastomers, to befitted into a thin cross sectional radial space between the shaft (18)and process chamber (5).

It is considered self evident from FIG. 3 that the invention can beoffered without the radial lip (29) on drive ring (21) and correspondingrecess (30) in sleeve (7). The invention without this supporting featureis shown in FIG. 7. If it is considered appropriate, the sleeve (7)deformation, as the result of radial force exerted by the packing (24)can be minimised by one or a combination of several factors. Suchfactors may include changing the materials of construction, reducing thesqueeze hence force applied on the packing (24) or designing sufficientradial relief in the inner diameter of the sleeve (7) to accommodate thedeformation. This principle has been illustrated in FIG. 5 for theinboard side of the sleeve (7) but could also be applied to the outboardside of the sleeve (7) if required.

FIG. 7 also illustrates a design without a positive drive mechanism. Theseal drive is transmitted through the metal to metal friction drive (54)by the screws (25) applying a compression load on sleeve (7) and drivering (21).

Similarly, FIG. 8 illustrates the inboard end of sleeve (7) with asupporting end cap (38) clamping the sleeve (7) with packing (9) and therotary seal face drive end (11) using screws (12). Clamp ring (38) hasan axially extending lip (39) which radially locates in recess (40) ofsleeve (7). This lip (39) supports the end of the sleeve (7) fromradially deforming under the force exerted by the packing (9) whencompressed. This is particularly important when the cartridge mechanicalseal is required to fit into a thin radial cross sectional space.

It has been surprising found that said end cap (38) could be offered inan exotic alloy material for increased chemical resistance. If requireda non-elastomeric gasket could be added in between the end cap (38) anddrive end (11) in area (41) to protect the sleeve (7) further. Thisoffers a commercial advantage.

By way of example only, FIG. 9 shows a partial cross section of analternate arrangement of the invention with a different outboard seal toshaft sealing arrangement. From FIG. 9 the sleeve (7) terminates in thevicinity of the drive ring (42). The dive ring (42) is secured to thesleeve (7) using radial screws (43). If required an appropriate relief(63) could be included in the sleeve (7). The packing (44) is compressedby the clamp ring (27) using screws (28). When the clamp ring (27)reaches its installed axial position it is secured to the shaft (18)using radial screws (45). The compressed packing (44) forms a leak tightseal between the shaft (18), the sleeve (7), drive ring (42) and clampring (27).

By way of example only, FIG. 10 shows a partial cross section of analternate arrangement of the invention with a different outboard seal toshaft sealing arrangement. From FIG. 10 the sleeve (7) terminates in thevicinity of the split drive ring (46). The split drive ring (46) isradially supported by locking collar (47) which extends radiallyoutwardly to the split drive ring (46). This arrangement ensures thatthe radial inwardly protruding lug (48) in the split drive ring (46)engages in the radial grove (49) in the sleeve (7) and thereby providesaxial positioning.

Spacer ring (50) radially engages into the drive ring (46) and acts tocompress packing (51) when screws (52) are secured. Screws (52) locatedin clamp ring (53).

By way of example only, FIG. 11 illustrates the invention applied to adouble cartridge mechanical seal. From FIG. 11 the stationary andaxially floating seal face (2) is spring biased towards an axiallystatic rotary seal face (1). The rotary face (1) is allowed to slide onthe stationary seal face (2). The interface between the rotary face (1)and stationary seal face (2) forms sealing area (3). This sealing area(3) is the primary seal that prevents the process media (4) fromescaping from the process chamber (5).

The second primary seal is made in the barrier media chamber (55) on theoutboard side of the mechanical seal. The stationary and axiallyfloating seal face (56) is spring biased towards an axially staticrotary seal face (57). The rotary face (57) is allowed to slide on thestationary seal face (56). The interface between the rotary seal face(57) and stationary seal face (56) forms sealing area (58). This sealingarea (58) is the primary seal that prevents the barrier media fromescaping from the barrier media chamber (55).

Secondary sealing members in contact with the process media includepacking members (59, 60 and 61). As described previously, the processmedia is allowed to travel in the radial gap (62) between the shaft (18)and the sleeve (7). It then is sealed by two further secondary packingmembers (17 and 24) as described in detail previously.

FIG. 11 clearly illustrates the invention applies to yet another inboardseal configuration. It is therefore clear that the invention can beapplied to any arrangement with a very thin radial cross sectionalsleeve. For reference the invention could be applied to a sleeve with aradial cross section as small as 0.020″ (0.5 mm).

By way of example only, FIG. 12 illustrates the invention applied to theatmospheric side of a “non-mechanical” design. One or more packingmember's (63) are radially outwardly positioned on sleeve (7). Thepacking member (63) forms a sliding contracting seal between the presschamber (5) and outer radial portion of the sleeve (7). Said packingmember's (63) are compressed in position by the gland (15) and bolts(64). This arrangement prevents the process media (4) form escaping fromthe process chamber (5).

The sleeve (7) to shaft (18) area is sealed by the invention assembly(65) as described previously.

FIG. 13 illustrates an alternative arrangement of the invention, Thesplit drive ring (46) has a radially inwardly protrusion (67) thatlocates into a radial recess (67) of sleeve (7). The split drive ring(46) is radially restrained by support ring (47). This arrangementensures that the protrusion (67) can not disengage from recess (68). Thespilt drive ring (46) has an appropriate positive drive mechanism totransmit the rotational drive into the sleeve (7). Radial screws (66)axially connect the split drive ring (46) to clamp ring (27). Theprocess media (4) is sealed when the packing member (44) is compressedby push ring (69) and axial screws (28).

It is considered self evident to the experienced reader that theinvention may be employed for both Rotary seals and Stationary seals,single, double or triple mechanical seals, whether designed in acartridge or component seal format. It is also considered self evidentthat the invention may be used with metallic components as well asnon-metallic components. Some types of equipment rotate the housing andhave a stationary shaft. It is considered that the invention can besimilarly applied to such designs. The invention may also be applied toa non-mechanical seal design, an example of which is illustrated in FIG.12.

1. A seal that provides sealing between a rotatable shaft and a housing,comprising: a stationary part connected to the housing and a rotary partfor rotation with the shaft, said rotary part comprising a sleevemounted on the shaft, one end of the sleeve comprising a non-elastomericsealing arrangement, said sealing arrangement comprising sealingsurfaces that contact the outer circumferential surfaces of the sleeveand the shaft and means for effecting sealing engagement between each ofsaid sleeve and said shaft and a respective sealing surface; wherein acomponent of the seal is axially secured to another component of theseal, a first one of said components having an axially extendingprotrusion which radially locates in an axially extending recess, saidfirst component supporting the other component in the vicinity of apacking member.
 2. A seal according to claim 1, wherein the seal is amechanical seal.
 3. A seal according to claim 1, wherein the radialspace cross section between the rotatable shaft and housing is at least0.312″ (7.9 mm).
 4. A seal according to claim 1, wherein the sleeve isradially supported at one or more points along its axial length.
 5. Aseal according to claim 1, wherein the sleeve is positively driven atone or more points along its axial length.
 6. A seal according to claim1, wherein a component of the seal has a radially disposed reliefdirectly adjacent to a packing member.
 7. A seal according to claim 1,wherein said components comprise different materials.
 8. A sealaccording to claim 1, wherein one component of the seal, located incontact with process media, has a radially disposed groove toaccommodate a sacrificial component.